This project is primarily concerned with the behavioral analysis of information transmission within the spinal somesthetic pathways, and this will be achieved by obtaining psychophysical data before and after a variety of interventions in the central nervous system. The subjects will be monkeys. The sensory tests will assess a variety of capacities: spatio-tactile discrimination, pain tolerance and detection, and sensory-motor coordination. Stimulation and lesion of the thalamus and spinal cord will be used to determine the behavioral significance of the different somesthetic pathways and nuclei. Evoked potentials and single cell recordings will also be obtained from these pathways and nuclei before and after stimulation or lesion of the brain or spinal cord. The neurophysiological studies will be aimed at discovering changes in the activity of intact pathways that result from interruption of activation of other, related structures.